Compact lidar system

ABSTRACT

An FM LIDAR system is described that includes a frequency modulated LIDAR system that incorporates a laser source that is optically coupled to a whispering gallery mode optical resonator. Light from the laser that is coupled into the whispering gallery mode optical resonator is coupled back out as a returning counterpropagating wave having a frequency characteristic of a whispering gallery mode of the optical resonator. This returning wave is used to reduce the linewidth of the source laser by optical injection. Modulation of the optical properties of the whispering gallery mode optical resonator results in modulation of the frequency of the frequencies supported by whispering gallery modes of the resonator, and provides a method for producing highly linear and reproducible optical chirps that are highly suited for use in a LIDAR system. Methods of using such an FM LIDAR system and vehicle assisting systems that incorporate such FM LIDAR systems are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/092,134, filed on Apr. 6, 2016 and entitled “COMPACT LIDAR SYSTEM”,which claims priority to U.S. Provisional Patent Application No.62/143,912, filed on Apr. 7, 2015 and entitled “Compact LIDAR System”.The entireties of these applications are incorporated herein byreference.

FIELD OF THE INVENTION

The field of the invention is LIDAR systems, particularly frequencymodulated continuous wave LIDAR systems.

BACKGROUND

The background description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art or relevant to thepresently claimed invention, or that any publication specifically orimplicitly referenced is prior art.

LIDAR is increasingly used for distance measurement in a variety ofapplications, ranging from cartography to microscopy. The incorporationof such functionality into an ever-growing range of devices, includingautonomous or semi-autonomous vehicles has led to the development ofincreasingly compact and low power consumption devices. At the sametime, demand for LIDAR devices with increased range and improvedresolution continues to grow.

LIDAR can be accomplished in a variety of ways. In “time of flight”(TOF) LIDAR short pulses of light are emitted and reflected pulsesreceived, with the delay between emission and reception providing ameasure of distance between the emitter and the reflecting object. SuchTOF systems, however, have a number of disadvantages. For example,simple TOF measurements are highly susceptible to interference fromother signal sources. This issue becomes more pronounced as the distancebetween the emitter and the reflecting object increases, as suchdistance necessarily decreases the strength of the reflected signal. Onthe other hand, inherent limitations in accurately measuring extremelyshort time intervals limit the spatial resolution of such TOF LIDARsystems at close range. In addition, the range of such TOF LIDARs is afunction of the ability to detect the relatively faint reflected signal.The resulting range limitations are frequently addressed by using highlysensitive photodetectors. In some instances such detectors can detectsingle photons. Unfortunately this high degree of sensitivity also leadsto increased misidentification of interfering signals as reflect TOFLIDAR pulses. Despite these disadvantages TOF LIDAR systems currentlyfind wide application, primarily due to the ability to provide suchsystems in a very compact format and the ability to utilize relativelyinexpensive non-coherent laser light sources.

Alternatives to TOF LIDAR have been developed. One of these, frequencymodulated (FM) LIDAR, relies on a coherent laser source to generaterepeated brief “chirps” of time delimited, frequency modulated opticalenergy. The frequency within each chirp varies linearly, and measurementof the phase and frequency of an echoing chirp relative to a referencesignal provides a measure of distance and velocity of the reflectingobject relative to the emitter. Other properties of the reflected chirp(for example, intensity) can be related to color, surface texture, orcomposition of the reflecting surface. In addition, such FM LIDARs arerelatively immune to interfering light sources (which tend to producenon-modulated signals) and do not require the use of highly sensitivephotodetectors.

The accuracy of this measurement depends upon a number of factors,including the linewidth limitations of the emitting laser, the range offrequencies (i.e. bandwidth) within the chirp, the linearity of thefrequency change during each chirp, and the reproducibility ofindividual chirps. Unfortunately, improvement in one of these factors isgenerally at the detriment of the remaining factors. For example, whileincreasing the bandwidth of the chirps improves resolution, doing somakes it difficult to maintain linearity of the frequency change withinthe chirp. Similarly, lasers that have a narrow linewidth can be poorlysuited for production of the range frequencies required to generate achirp. In addition, FM LIDAR systems that have been developed to dateare far from compact, as they rely on relatively large FMCW lasersources. In addition, such systems typically rely on a carefullymodulated, low noise local oscillator (for example, a narrow linewidthsolid state, gas, or fiber laser) with frequency modulationcorresponding to that of the emitted chirp provided by a relativelylarge interferometer. This local oscillator precisely replicates anemitted chirp, and serves as the reference for the received reflectedchirp. As a result FM LIDARs are relatively large, complex, andexpensive, and have seen limited implementation relative to TOF LIDARsdespite their performance advantages.

Quack et al (presentation at GOMACTech, St. Louis, Mo., USA, Mar. 23-26,2015) have proposed development of a FMCW LIDAR source device that wouldrequire construction and integration of an electromechanically modulatedlaser source, an optical interferometer, and modulating electronics on asingle silicon chip. The resulting device however, relies on anelectronic feedback system that inherently generates nonlinear opticalchirps. This is only partially corrected by applying a “pre-distorting”the feedback signal supplied to the laser source and utilization of anexternal reference frequency generator that can act as an additionalsource of variation (Satyan et al, Optics Express vol. 17, 2009). Theresulting LIDAR source is highly complex, and it remains to be seen ifsuch diverse features can be successfully integrated on a single siliconchip in a reliable fashion. In addition, a LIDAR incorporating such asource is still reliant on the use of a complex local oscillator toprovide useful data.

Thus there is a need for a compact, robust, and efficient LIDAR systemthat exhibits a high degree of chirp linearity, large chirp bandwidth,and high chirp reproducibility.

The following description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art or relevant to thepresently claimed invention, or that any publication specifically orimplicitly referenced is prior art.

SUMMARY

Embodiments of the inventive concept include a frequency modulated LIDARsystem that incorporates a laser source that is optically coupled to awhispering gallery mode optical resonator. Light from the laser that iscoupled into the whispering gallery mode optical resonator is coupledback out as a returning counterpropagating wave having a frequencycharacteristic of a whispering gallery mode of the optical resonator.This returning wave is used to reduce the linewidth of the source laserby optical injection. Modulation of the optical properties of thewhispering gallery mode optical resonator results in modulation of thefrequency of the frequencies supported by whispering gallery modes ofthe resonator, and provides a method for producing highly linear andreproducible optical chirps that are highly suited for use in a LIDARsystem.

One embodiment of the inventive concept is a LIDAR system that includesa laser light source, a modulatable whispering gallery mode resonatorthat is optically coupled to the laser light source to provide linewidthreduction via optical injection, a transducer that can alter an opticalproperty of the whispering gallery mode optical resonator (for example,refractive index), a controller that controls the transducer, atransmission assembly for transmitting optical chirps generated by thecontroller, a receiver that receives reflected optical chirps, and aprocessor that utilizes data derived from the reflected chirps todetermine position of an object that is reflecting the chirps. In someembodiments all of these components are provided on a single substrate.The linewidth of the optical injection locked laser source can be lessthan 1 kHz. In a preferred embodiment, the laser source can also act asthe source of a reference chirp that is combined with a reflected chirpin determining position of a reflecting object.

Another embodiment of the inventive concept is a method of utilizing aLIDAR system. In such methods LIDAR system that includes a laser lightsource, a modulatable whispering gallery mode resonator that isoptically coupled to the laser light source to provide linewidthreduction via optical injection, a transducer that can alter an opticalproperty of the whispering gallery mode optical resonator (for example,refractive index), a controller that controls the transducer, atransmission assembly for transmitting optical chirps generated by thecontroller, a receiver that receives reflected optical chirps, and aprocessor that utilizes data derived from the reflected chirps todetermine position of an object that is reflecting the chirps isprovided. A reference chirp that is also produced by the laser source iscompared with a chirp reflected by a reflective object within range ofthe LIDAR system to determine the position of the reflective object.

Another embodiment of the inventive concept is a vehicle assistancesystem that incorporates a LIDAR system that includes a laser lightsource, a modulatable whispering gallery mode resonator that isoptically coupled to the laser light source to provide linewidthreduction via optical injection, a transducer that can alter an opticalproperty of the whispering gallery mode optical resonator (for example,refractive index), a controller that controls the transducer, atransmission assembly for transmitting optical chirps generated by thecontroller, a receiver that receives reflected optical chirps, and aprocessor that utilizes data derived from the reflected chirps todetermine position of an object that is reflecting the chirps, and anassistive engine that receives data produced by the LIDAR and that is incommunication with a vehicle effector. Such an effector can be anotification system for use by a vehicle operator. In some embodimentsthe effector is coupled to a transducer that affects vehicle operation(e.g. steering, engine speed, etc.). In some embodiments the vehicle iscontrolled by an operator, who can be present in the vehicle oroperating it remotely. In other embodiments the vehicle is autonomous.Various objects, features, aspects and advantages of the inventivesubject matter will become more apparent from the following detaileddescription of preferred embodiments, along with the accompanyingdrawing FIG.s in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic of an embodiment of a device that supportsinjection locking of a laser using an optical resonator.

FIG. 2 depicts a schematic of an alternative embodiment of a device thatsupports injection locking of a laser using an optical resonator.

FIG. 3 depicts a schematic of another alternative embodiment of a devicethat supports injection locking of a laser using an optical resonator.

FIGS. 4A to 4D depict configurations for exemplary optical resonators.FIG. 4A depicts a spherical optical resonator. FIG. 4B depicts anannular optical resonator with a convex outer face. FIG. 4C depicts adiscoidal optical resonator. FIG. 4D depicts annular optical resonatorwith a planar outer face.

FIGS. 5A and 5B depict placement of electrodes on an optical resonator.FIG. 5A schematically depicts a discoidal optical resonator with anelectrode applied at the perimeter. FIG. 5B schematically depicts amodulated whispering gallery mode optical resonator 560 includes adiscoidal optical resonator 565 with electrodes 570, 580 applied toopposing planar faces of the resonator.

FIGS. 6A to 6D depicts various implementations of an optical resonatorintegrated into a silicon chip. FIG. 6A depicts a spherical opticalresonator that is optically coupled to waveguides generated on a siliconchip. FIG. 6B depicts a discoidal optical resonator generated on asilicon chip and optically coupled to a waveguide generated on the samesilicon chip. The waveguides are in turn optically coupled to anadjacent silicon chip. FIG. 6C depicts a ring optical resonatorgenerated on a silicon chip and optically coupled to a waveguidegenerated on the same silicon chip. The waveguides are in turn opticallycoupled to an adjacent silicon chip. FIG. 6D depicts a spherical opticalresonator optically coupled to a pair of GRIN lenses, which are in turnoptically coupled to waveguides generated on a silicon chip.

FIGS. 7A and 7B depict emitted and reflected linear, monotonic opticalfrequency chirps. FIG. 7A shows changes in optical frequency over timefor an emitted optical frequency chirp and a returning, reflectedoptical frequency chirp. FIG. 7B shows the result of fast Fouriertransform processing of typical data.

FIGS. 8A and 8B depict emitted and reflected biphasic linear opticalfrequency chirps. FIG. 7A shows changes in optical frequency over timefor an emitted optical frequency chirp and a returning, reflectedoptical frequency chirp. FIG. 7B shows the result of fast Fouriertransform processing of typical data.

FIG. 9 depicts a complex biphasic optical frequency chirp, wherefrequency varies with time in a sigmoidal fashion.

FIG. 10 schematically depicts a LIDAR system of the inventive concept.

FIG. 11 schematically depicts an Automated Driving Assistance System(ADAS) incorporating a LIDAR of the inventive concept.

DETAILED DESCRIPTION

The following description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art or relevant to thepresently claimed invention, or that any publication specifically orimplicitly referenced is prior art.

The inventive subject matter provides apparatus, systems and methods inwhich a LIDAR system is based upon a FMCW laser light source that islocked to a whispering gallery mode resonator by optical injection. Thisprovides a laser source with an exceptionally narrow linewidth, which(when used in conjunction with a whispering gallery mode opticalresonator having controllable optical properties) permits the generationof large bandwidth, highly linear, and highly reproducible chirps by asimple and direct optical mechanism. Such a frequency modulated (FM)LIDAR does not require the use of a separate local oscillator, but canutilize a beam splitter (or functional equivalent) to provide areference FM signal from the injection locked FMCW laser. Such LIDARsystems can be compact and can be produced economically on a siliconwafer using photolithographic methods. Linearity of the chirps producedin such a system can be less than 10% to less than 0.2%. Bandwidth ofthe chirps produced can be 10 GHz or greater, the signal to noise rationcan be as low as 10 dB with a laser power as low as 3 mW, which canprovide a range of up to 200 meters or more.

Various objects, features, aspects and advantages of the inventivesubject matter will become more apparent from the following detaileddescription of preferred embodiments, along with the accompanyingdrawing figures in which like numerals represent like components.

In some embodiments, the numbers expressing quantities of ingredients,properties such as concentration, reaction conditions, and so forth,used to describe and claim certain embodiments of the invention are tobe understood as being modified in some instances by the term “about.”Accordingly, in some embodiments, the numerical parameters set forth inthe written description and attached claims are approximations that canvary depending upon the desired properties sought to be obtained by aparticular embodiment. In some embodiments, the numerical parametersshould be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof some embodiments of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspracticable. The numerical values presented in some embodiments of theinvention may contain certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.

As used in the description herein and throughout the claims that follow,the meaning of “a,” “an,” and “the” includes plural reference unless thecontext clearly dictates otherwise. Also, as used in the descriptionherein, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

The recitation of ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g. “such as”) provided with respectto certain embodiments herein is intended merely to better illuminatethe invention and does not pose a limitation on the scope of theinvention otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element essential to thepractice of the invention.

Groupings of alternative elements or embodiments of the inventiondisclosed herein are not to be construed as limitations. Each groupmember can be referred to and claimed individually or in any combinationwith other members of the group or other elements found herein. One ormore members of a group can be included in, or deleted from, a group forreasons of convenience and/or patentability. When any such inclusion ordeletion occurs, the specification is herein deemed to contain the groupas modified thus fulfilling the written description of all Markushgroups used in the appended claims.

One should appreciate that the disclosed techniques provide manyadvantageous technical effects including the provision of accurate andefficient LIDAR systems, which can be manufactured economically on asingle wafer or chip using conventional photolithographic techniques.

The following discussion provides many example embodiments of theinventive subject matter. Although each embodiment represents a singlecombination of inventive elements, the inventive subject matter isconsidered to include all possible combinations of the disclosedelements. Thus if one embodiment comprises elements A, B, and C, and asecond embodiment comprises elements B and D, then the inventive subjectmatter is also considered to include other remaining combinations of A,B, C, or D, even if not explicitly disclosed.

As used herein, and unless the context dictates otherwise, the term“coupled to” is intended to include both direct coupling (in which twoelements that are coupled to each other contact each other) and indirectcoupling (in which at least one additional element is located betweenthe two elements). Therefore, the terms “coupled to” and “coupled with”are used synonymously.

In frequency modulated continuous wave (FMCW) LIDAR, narrow linewidth FMlaser light is modulated to provide a frequency ramp, for example anexponential ramp, linear ramp, and or a sigmoidal ramp. Such ramps canbe monotonic (i.e. trending in only one direction), bimodal, ormultimodal. In some embodiments a linearly ramping frequency rampgenerates a linear optical chirp. Such a linear chirp can be transmittedthrough a beam splitter, and a portion of the chirp emitted. Onencountering an object the emitted chirp can be reflected and receivedby the FMCW LIDAR system as a reflected chirp. This reflected chirp canbe combined with a reference chirp obtained from the FM laser (forexample, via the beam splitter), for example by translating the receivedreflected chirp and the reference chirp into FM electrical currents viaphotodetectors and combining them in an amplifier. The combined signalcan be processed (for example using a fast Fourier transform) tocharacterize differences in phase and/or frequency between the signals,thereby providing measurement of a reflecting object's distance and/orspeed. The performance (i.e. range resolution and accuracy) of such anFMCW LIDAR system is directly related to the bandwidth of the frequencyramp, as shown in Formula 1, where ΔR is the range resolution, c is thespeed of light, and B is the bandwidth of the emitted frequency chirp:

ΔR=c/2B  Formula 1

Essentially, the greater the bandwidth of the chirp, the better therange resolution. Performance is impacted by the linearity of thefrequency ramp or change throughout the chirp, with deviations fromlinearity resulting in poor reproducibility between chirps. Suchlinearity is negatively impacted by increasing linewidth of the lasersource. If the applied ramp is not highly linear, the quality of theresulting interference data is poor. If a nonlinear frequency ramp isutilized (for example, a sigmoidal change in frequency over time),consistency of the nonlinear function is similarly important. Similarly,variation in the amplitude of the light provided by the laser (relativeintensity noise, or RIN) can degrade FM LIDAR performance.Unfortunately, laser sources commonly used for FM LIDAR have relativelylarge RIN. For an effective system both an extended bandwidth for themodulated frequency of the chirp and high linearity within the chirp areneeded. Unfortunately, the greater the bandwidth of a frequency chirpthe more difficult it is to linearize it and/or produce it consistently.

Systems and devices of the inventive concept utilize an FMCW laser lightsource that is optically coupled to an optical resonator that supportswhispering gallery modes corresponding to one or more wavelengthsemitted by the laser. A portion of the light trapped within the opticalresonator as whispering gallery mode frequency is returned to the laserto provide optical injection locking. This serves to both reduce thelinewidth of the laser output, but also to reduce RIN by at least afactor of 10 (relative to the source laser without such opticalinjection locking). The resulting laser output can have extremely narrowlinewidths (for example, 1,000 HZ, 500 Hz, 250 Hz, 100 Hz, or less than100 Hz). Such a laser source can provide linear chirps with largebandwidths (for example, 1 GHz, 5 GHz, 10 GHz, 15 GHz, or more), and canprovide a range resolution of (10 cm, 7.5 cm. 5 cm, 2.5 cm, 1 cm, orless than 1 cm). Such range resolutions are useful for a wide variety ofapplications, including portable devices, autonomous and semi-autonomoustransportation, augmented and virtual reality systems, and imagingsystems. It should be appreciated that a 15 GHz bandwidth within alinear chirp is equivalent to 150 million times a 100 Hz laserlinewidth. Such a signal can be easily discerned, and a high degree oflinearization over a large bandwidth can be achieved. For comparison, aprior art system utilizing a typical FM laser with a linewidth of 1 nmwould have to be utilize a chirp having a frequency ramp correspondingto some tens of nanometers (for example, 50 nm) to provide adequatedistinction, and still would not provide a comparable resolution andsignal to noise ratio. It should also be appreciated that linearizingsuch a 50 nm bandwidth chirp would be extremely technically challenging.Similar issues arise when using a typical prior art laser light sourcehaving a linewidth of 100 kHz or more. Inventors have found that the useof a very narrow linewidth laser light source can improve LIDARperformance, while selection of an appropriate method narrowinglinewidth while also providing highly controllable and replicatablefrequency modulation can simplify the architecture, operation, andultimately the cost of production of a LIDAR system. In a preferredembodiment, all or at least the majority of the components of a laserlight source having the performance characteristics described above andthe remaining components of the LIDAR system can be manufactured on asilicon chip using photolithographic techniques.

The linearity of, for example, a monotonic chirp of increasingfrequency, can be expressed as the r value of a correlation between themeasured frequency vs ideal frequency for a series of time points for agenerated chirp. For example if the desired profile of an optical chirpis as shown in FIG. 7A, which shows a monotonic and linear increase infrequency over time, linearity can be expressed as the correlationbetween measured and desired or optimal frequency at corresponding timepoints. In such an example, a perfectly linear generated chirp would beexpected to produce an r value of 1 in such a correlation. Deviationsfrom ideal behavior (for example, curvilinear deviation at the beginningand/or end of the chirp, would result in r values that are less than 1.Similar correlation studies can be performed for bimodal chirps andnonlinear (e.g. sigmoidal) chirps. In embodiments of the inventiveconcept linearity of produced chirps can produce r values greater than0.8, greater than 0.85, greater than 0.88, greater than 0.9, greaterthan 0.92, greater than 0.95, greater than 0.97, greater than 0.98,greater than 0.99, and/or greater than 0.995 over the frequency range ofthe generated chirp.

Similarly, variation between produced chirps should be minimized. Chirpscan be characterized by a number of quantifiable factors, includingduration, frequency distribution, amplitude, and deviations fromlinearity (as described above). Variation within a population of chirpscan be expressed as a standard deviation and/or coefficient of variation(CV) surrounding a central value for such quantifiable factors. Inembodiments of the inventive concept, a CV for duration, frequencydistribution, amplitude, and/or deviation from linearity for astatistically significant group of chirps (e.g. greater than 32) canhave a C.V. of less than 25%, less than 20%, less than 15%, less than10%, less than 7.5%, less than 5%, less than 2.5%, less than 1%, lessthan 0.5%, less than 0.25%, less than 0.2%, and/or less than 0.1%.

In some embodiments of the inventive concept a suitable laser lightsource for a LIDAR system can be provided by optically coupling a laserlight source to an optical resonator. Such an optical resonator can bedimensioned and constructed of materials that support a whisperinggallery mode at a wavelength that is emitted by a source laser, and canbe constructed of materials (for example electro-optical materials) thatpermit controlled modulation of an optical property (for examplerefractive index) of the optical resonator. Modulation of the opticalproperty of the whispering gallery mode resonator (for example, byapplication of an electrical potential, change of temperature, and/ormechanical pressure) can alter the frequency of the whispering gallerymode. Light can be coupled from an FMCW laser source into a whisperinggallery mode by evanescent wave coupling, for example using a prism, anoptical fiber with a faceted face, or similar device. Similarly, lightfrom a counterpropagating whispering gallery mode wave within theoptical resonator can be coupled out and returned to the source laser toprovide optical injection locking, which in turn provides a narrowlinewidth laser output. Modulation of the optical property of theoptical resonator (for example, via electrodes, a resistive heater,and/or a piezoelectric device) alters the frequency supported by thewhispering gallery mode. This in turn alters the frequency utilized foroptical injection locking and results in modulating the frequency outputof the laser, which continues to have a very narrow linewidth.

As a result in such an arrangement, controlled modulation of the opticalproperties of a whispering gallery mode resonator in opticalcommunication with an FMCW laser (for example, by a chirp generatorprogrammed to produce one or more chirp patterns and intervals) permitsdirect generation of highly linear (or highly consistently nonlinear)frequency chirps through optical means. The high degree ofreproducibility and narrow linewidth of the resulting laser emissionspermits the use a simple beam splitter (or similar device) to provide aLIDAR system wherein the modulated FMCW laser serving as the source ofan emitted chirp used to characterize a reflecting object can also serveas the source of the reference chirp used to characterize the returningreflected chirp. It should be appreciated that this greatly reduces thecomplexity and size of the resulting LIDAR system. In some embodimentsof the inventive concept highly reproducible frequency chirps can beproduced by altering the optical properties of the optical resonator ina controlled fashion, for example by application of current to theoptical resonator, application of pressure to the optical resonator,and/or altering the temperature of the optical resonator. It should beappreciated that such an arrangement permits generation of a widevariety of frequency chirp configurations, which can be suitable fordifferent applications.

A variety of configurations are suitable for optically coupling a lasersource and a whispering gallery mode resonator in this fashion. Oneexample is shown in FIG. 1, which depicts an arrangement with a set offeedback optics 8. In the arrangement shown in FIG. 1, a source laser 1provides a laser beam la that is coupled into a whispering gallery moderesonator 4 (WGM resonator) using an optical coupler 4 a, for example aprism. In some embodiments the laser beam is passed through a phaserotator 2 and directed into the optical coupler using a lens 3. A subsetof the frequencies represented in the laser beam propagates as aself-reinforcing whispering gallery mode wave 5 a through the resonatorthat is “captured” in the whispering gallery mode. A portion of thispropagated light is coupled out of the WGM resonator by a second opticalcoupler 4 b, and the output light beam 6 a reflected by a mirror 8 a(which can be provided on a mount 8 c) to provide a reflected light beam6 b. In some embodiments the output light beam and/or the reflectedlight beam are directed with a lens 8 b. The reflected light beam iscoupled back into the WGM resonator to form a counterpropagating wave 5b. This can be coupled out of the resonator by the first optical couplerand returned to the source laser as a feedback light 1 b, where opticalinjection results in a narrowed linewidth laser output 7. The narrowedlinewidth output of the source laser can be output through an exposedfacet of the first prism and utilized in a LIDAR system.

In other embodiments of the inventive concept, optical coupling betweena source laser and an optical resonator and between the opticalresonator and a reflector that provides a counterpropagating wave by awaveguide. Suitable waveguides include optical fibers and opticallyconductive materials provided on silicon wafers. An example of such anembodiment is shown schematically in FIG. 2. As shown, a source laser200 can be coupled to a whispering gallery mode resonator 240, using oneor more waveguides 210, 230. In some embodiments a collimator or opticalmode selector 220 can be interposed between the laser and the whisperinggallery mode resonator. Light from the laser is coupled into thewhispering gallery mode resonator, where light corresponding to thewhispering gallery mode(s) is entrapped. At least a portion of theentrapped light is coupled out of the whispering gallery mode resonatorto a waveguide 250, where it is directed towards a reflector. In someembodiments a collimator or optical mode selector 260 is interposedbetween the whispering gallery mode resonator and the reflector, withoptical communication provided by an additional waveguide 270. Lightreturned from the reflector is coupled back into the whispering gallerymode resonator, and back into an optical path that directs it towardsthe laser. This returning light provides optical injection locking ofthe laser to a frequency corresponding to a whispering gallery mode ofthe resonator to provide a laser output 290 with a narrowed linewidthcompared to that of the source laser without such optical injectionlocking. In some embodiments these components can be provided on asingle integrated chip 295.

In some embodiments, optical filters can be incorporated into thedevice. FIG. 3 shows an example with an optical arrangement similar tothat depicted in FIG. 1, but incorporating an optical spatial filterbetween the second prism and the reflector in order to improve thespatial distribution of the beam. A laser source 300, which can includea reflector 305, provides light that is transferred to a whisperinggallery mode resonator 320 by an optical coupler 315. In someembodiments a collimator or optical mode selector 310 is interposedbetween the laser and the optical coupler. Light corresponding to awhispering gallery mode of the resonator is entrapped within theresonator, and at least a portion is coupled out of the resonator by asecond optical coupler 325 and directed to a set of feedback optics 327.These feedback optics can include a reflector 340 and an optical spatialfilter 335 (for example, a pinhole) placed between the second opticalcoupler and the reflector of the feedback optics. In some embodiments acollimator or optical mode selector can be placed between the secondoptical coupler and the optical spatial filter. Light reflected from thereflector of the feedback optics is coupled back into the whisperinggallery mode optical resonator to provide a counterpropagating wave. Atleast a portion of this counterpropagating wave is transferred out ofthe whispering gallery mode resonator and directed back towards thelaser, providing optical injection that results in a narrowing of thelinewidth of the laser. This narrow linewidth output is provided as anoutput laser beam 345. In some embodiments a control circuit 350 isprovided that permits modulation of the laser.

While the examples shown utilize a reflector to provide acounterpropagating wave within the optical resonator, other embodimentsof the inventive concept do not require the use of a mirror orreflector. For example, in some embodiments of the inventive conceptlight scattering within the material of a WGM resonator can provide acounterpropagating wave of sufficient intensity to be useful in opticalinjection locking of the source laser. In other embodiments features canbe introduced into and/or on the surface of a WGM resonator to provide acounterpropagating wave. Suitable features include inclusions within thebody of the WGM resonator, pits, channels, or other features generatedon the surface of the WGM resonator, and/or an optical grating generatedon the surface of the WGM resonator.

Suitable optical resonators are available in a variety ofconfigurations. As shown in FIGS. 4A, 4B, 4C, and 4D, suitableresonators can be configured in a variety of ways. As shown in FIG. 4A,a whispering gallery mode optical resonator 400 can be configured as asphere, having a circular cross section 410 and extending through a Zaxis 405. Alternatively, a whispering gallery mode resonator can beconfigured as a torus or toroidal solid, as shown in FIG. 4B. In FIG. 4Bthe whispering gallery mode optical resonator 415 has a circular crosssection 420 and extends along the Z axis 425 while having a centralaperture. In this example the outer wall of the whispering gallery modeoptical resonator has a convex profile, extending outwards from thecenter. Another example of a suitable configuration for a whisperinggallery mode optical resonator is shown in FIG. 4C. In FIG. 4C thewhispering gallery mode optical resonator 430 has a disc configuration,with a circular cross section and a height 455 that defines a topsurface 435, an outer surface 445, an edge 450, and a lower surface 440.Such an edge can describe an angle of about 90° (e.g. from about 70° toabout 90°), and in some embodiments can present as sharp edges. FIG. 4Ddepicts an alternative toroidal configuration for a whispering gallerymode optical resonator, which resembles a disc with a central aperture.As shown the whispering gallery mode optical resonator 460 can beessentially circular and includes a central aperture 465, with a width495 defined by the radius of the aperture. Such a whispering gallerymode optical resonator includes an upper surface, 470, a lower surface475 and an outer wall 480 with a height 490. The edge 497 of the outerwall can have an angle of about 90° (e.g. from about 70° to about 90°),and in some embodiments can be a sharp edge.

In some embodiments of the inventive concept the whispering gallery moderesonator can be modulated. For example, a whispering gallery moderesonator in a LIDAR system of the inventive concept can be constructedof a material with a refractive index that changes on the application ofheat, pressure, and/or electrical potential. In such embodiments awhispering gallery mode resonator can be coupled to a transducer, suchas a resistance heater, a piezoelectric device, and/or an electrode.Examples of whispering gallery mode optical resonators that are coupledto transducers in the form of electrodes are shown in FIGS. 5A and 5B.FIG. 5A shows an electronically modulated resonator assembly 500 thatincludes a whispering gallery mode optical resonator 510 constructed ofan electro-optical material, which is in contact with an electrode pair520, 530. The electrode pair is in electronic communication with acontroller 540 that can apply a current and/or voltage potential to theelectrode pair, thereby modifying the refractive index of the whisperinggallery mode optical resonator (and thereby altering the frequenciessupported in whispering gallery mode). Such an assembly can also includean optical interface 545 (e.g. a prism or waveguide with anappropriately angled interface surface) that can transmit incoming light550 and couple it into the whispering gallery mode optical resonator. Itshould be appreciated that modulation of such a whispering gallery moderesonator in a LIDAR system of the inventive concept can providemodulation of the laser source that is locked to the whispering gallerymode resonator via optical injection locking. As a result, changes inthe refractive index of the optical resonator that result in a change inthe frequency supported by the whispering gallery mode can result ininjection locking of the source laser at new wavelength while retainingnarrow linewidth.

Inventors have found that injection locking of a source laser usinglight extracted from an optically coupled whispering gallery moderesonator provides a means for generating highly linear optical chirpsthat incorporate a broad range of frequencies, via modulation of theoptical properties of the resonator. As noted above, the opticalproperties of such resonators can be directly modulated by applicationof a voltage potential, change in temperature, application of pressure,or a combination of these. Such modulation can alter the frequencysupported by the whispering gallery mode(s) of the resonator, therebyaltering the frequency utilized for injection locking of the sourcelaser and subsequently locking the laser to the altered frequency. Forexample, application of a gradient (e.g. a linear, bimodal, and/orsigmoidal gradient) of voltage to such a whispering gallery mode opticalresonator over a defined time course results in the generation of anoptical chirp corresponding to the applied gradient, through purelyoptical effects.

In embodiments of the inventive concept the source laser, opticalresonator, waveguides for optical coupling of optical components,associated electronic circuitry to power the laser and control theoptical resonator, an optical scanning and receiving subsystem, andelectronic circuitry providing data analysis can be fabricated on one ormore distinct supports (for example, circuit boards, silicon chips, orcombinations thereof). For example, a subset of system components (forexample, a laser, a whispering gallery mode resonator, and associatedoptical couplings) can be fabricated on a first support, an opticalscanning subsystem fabricated on a second support, control circuitrythat directs the activity of the optical resonator and the scanningsubsystem fabricated on a third support, and integrated circuitsproviding conversion of incoming reference and/or reflected chirps intoelectronic data and for analysis of such electronic data fabricated on afourth support, with appropriate optical and electronic connectionsproviding communication between these different supports in theassembled system. It should be appreciated that other combinations ofsystem components on two or more supports are contemplated.

In other embodiments all functional elements of the LIDAR system (e.g. alaser and optically coupled whispering gallery mode resonator, opticalscanning and receiving subassembly, control circuitry, conversion ofincoming reference and/or reflected chirps to electronic data, and dataanalysis) can be fabricated on a single support (for example, a circuitboard or silicon chip). In some embodiments a flip chip fabricationmethod can be utilized, for example to incorporate a whispering gallerymode resonator. For example, integrated circuitry utilized to generatethe electronic signal used to modulate the optical characteristics ofthe optical resonator can be fabricated on the same silicon chip as thelaser and resonator, along with appropriate electrical connections.Components of a beam scanner (for example, a beam scanner incorporatingmonostatic optics) can be fabricated on the same silicon chip, alongwith waveguides that provide an optical connection to the frequencymodulated laser. Similarly, integrated circuitry utilized to controlscan timing (ex. a scan clock) can be fabricated on the silicon chip,along with appropriate electrical connections with the beam canner andthe chirp generating circuitry. Optical waveguides can also befabricated that provide optical communication between the beam scannerand a photocell, in order to provide transcription of a reflectedoptical chirp into a corresponding electronic return signal. Similaroptical waveguides can be fabricated to provide an optical connectionbetween the frequency modulated laser and a second photocell in order toprovide transcription of a transmitted optical chirp into acorresponding electronic transmitted signal. Such photocells can befabricated on a silicon chip, along with electrical connections to asimilarly fabricated amplifier. Amplified electronic reflected andtransmitted chirp signals can be directed from the amplifier tointegrated circuitry that provides fast Fourier transformation of thereceived signals, with the transformed data transferred to integratedcircuitry that processes such data to produce a LIDAR point cloud, withsuch integrated circuits also fabricated on a common silicon chip. Sucha device provides a complete, low power LIDAR device fabricated on asingle silicon chip.

A LIDAR system of the inventive concept can include a subassembly thatprovides a scanning function for directing the transmission of anemitted chirp and a receiving system for receiving an incoming,reflected chirp. A variety of mechanisms are suitable for providing thescanning function, including rotating or gimbal-mounted mirrors, MEMsdevices, a set of two or more mirrors mounted on actuators (for example,electric motors, solenoids, and or piezoelectric devices) in a mutuallyorthogonal fashion, rotating prisms, and/or rotating lenses. An exampleof a suitable MEMs device is the solid-state tripod mirror mountdeveloped by MinFaros®. In some embodiments a phased array steeringdevice can be used to provide a scanning function. Such a scanningfunction can be utilized to direct a series of transmitted chirps in apattern that sweeps an X-Y plane and/or interrogates a three-dimensionalvolume. Such a subassembly can also include a receiving system thatintercepts a reflected chirp and directs it (either directly orindirectly via a waveguide or similar device) towards a photocell forconversion to electronic data. Such a receiving system can include alens and/or mirror that is suitably positioned to intercept and direct areflected chirp. In some embodiments the position from which the emittedchirp leaves the LIDAR system and the position from which the reflectedchirp is received are coaxial. In other embodiments the position fromwhich the emitted chirp leaves the LIDAR system and the position fromwhich the reflected chirp is received are positioned on differentoptical axes. In a preferred embodiment the position from which theemitted chirp leaves the LIDAR system and the position from which thereflected chirp is received are coaxial and proximal, so as to provide acompact device.

Such compact, light weight FMCW LIDAR systems have wide application inportable devices and other systems where space, weight, and/or powerconsumption is at a premium. For example, such compact FMCW LIDARsystems can be utilized in piloted, autonomous, and/or semi-autonomousdrones, robotic systems, and enhanced reality VR systems. It should beappreciated that such FMCW LIDAR systems can provide information relatedto not only the position and speed of a reflecting object, but alsoinformation related to physical properties such as color, composition,and surface roughness. In this context, the term “position” wouldusually refer to relative spatial coordinates, but could alternativelybe limited to merely a measure of a magnitude of a distance.

As noted above, in preferred embodiments of the inventive concept, allor some of the components of the LIDAR system are provided on a wafer orchip comprising silicon or other appropriate material. Such componentscan be manufactured using photolithographic methods or a combination ofphotolithographic and conventional optical manufacturing techniques,including flip chip techniques. Production of the components ofprocessors and photodetectors on silicon surfaces is well known in theelectronics industry. Similarly, laser light sources (for example, adiode laser) can also be produced on a silicon substrate. Other opticaldevices, such as waveguides, can be provided on a silicon substrate, forexample by deposition of optically conductive materials usingphotolithographic methods. Similarly, WGM optical resonators can eitherbe produced on a silicon substrate or introduced to a prepared site on asilicon substrate and used in combination with such components toprovide an integrated LIDAR system. One example of such an embodiment isshown in FIG. 6A. In FIG. 6A, optical coupling into and out of aspherical WGM resonator is provided by optical waveguides generated on asilicon wafer or chip using photolithographic techniques. In thisexample, the WGM resonator is manufactured separately and integratedinto the LIDAR chip.

Another example is shown in FIG. 6B. In FIG. 6B, optical coupling intoand out of a discoidal WGM resonator is provided by optical waveguidesgenerated on a silicon wafer or chip using photolithographic techniques.In such an embodiment, the discoidal WGM resonator can be manufacturedseparately and integrated into the LIDAR chip, for example by placementin a cavity generated using photolithography. Alternatively, such adiscoidal WGM resonator can be produced on the surface of the siliconwafer or chip using photolithography and suitable dopants and/ordeposited optical materials.

Another example is shown in FIG. 6C. In FIG. 6C, optical coupling intoand out of a toroidal or ring-shaped WGM resonator is provided byoptical waveguides generated on a silicon wafer or chip usingphotolithographic techniques. In such an embodiment, the ring-shaped(i.e. a flattened torus) WGM resonator can be manufactured separatelyand integrated into the LIDAR chip, for example by placement in achannel generated using photolithography. Alternatively, such aring-shaped WGM resonator can be produced on the surface of the siliconwafer or chip using photolithography and suitable dopants and/ordeposition of optical materials.

In still other embodiments, a whispering gallery mode resonator can beintegrated into a LIDAR system on a silicon wafer or chip using alensing system. Such lenses can be manufactured on the surface of thesilicon wafer or chip by photolithographic techniques or, alternatively,manufactured separately and placed into suitable cavities prepared onthe silicon wafer or chip. An example of such an embodiment is shown inFIG. 6D. In FIG. 6D, a silicon waveguide produced on a silicon substrateprovides optical communication with a GRIN lens. The GRIN lens can bemanufactured separately and affixed to the silicon wafer or chip, or canbe produced on the silicon wafer or chip by photolithographic methods.The GRIN lens includes an angled facet. A similar GRIN lens with asimilar facet is provided, such that the angled facets of the pair ofGRIN lenses are oriented towards each other. A suitable opticalresonator is brought into optical communication with the GRIN lens bycontacting it to the angled facets. In some embodiments, gratingcouplers are provided to provide optical communication betweenwaveguides manufactured on the silicon wafer or chip and the GRINlenses.

An example of a linear optical frequency chirp suitable for use in LIDARis shown in FIG. 7A. As shown, an emitted chirp 710 that has a single,increasing trend in optical frequency over time is compared to anidentically configured returning optical frequency chirp 720 produced byreflection from a distant object. The difference 730 in frequencymeasured at a specific time point is characteristic of the distancebetween the LIDAR emitter and the detected reflecting object. As shownin FIG. 7B, a Fourier Transform analysis of signal power vs beat signalfrequency of data derived from such linear, monotonic optical chirpsprovides a power signal peak 740 that is indicative of the distancebetween the LIDAR emitter and the detected object.

Additional information can be derived from an optical frequency chirpthat has a bimodal or Δ configuration, i.e. having an increasingfrequency segment and a decreasing frequency segment, joined by aninflection point. An example of the use of such an optical frequencychirp is shown in FIG. 8A. In FIG. 8A an emitted chirp 810 is shownsuperimposed on a returning, echoed chirp 820. Different sets offrequency differences 830,840 are associated with the ascendingfrequency limb and the descending frequency limb of the chirp. In suchan embodiment, the ascending limb difference 830 can be associated withthe distance between the LIDAR emitter and the reflecting object, whilethe descending limb difference 840 can be associated with the relativevelocity between the LIDAR emitter and the reflecting object. As shownin FIG. 8B a Fourier Transform analysis of signal power vs beat signalfrequency of data derived from such optical chirps provides a powersignal peak 860 that is indicative of the distance between the LIDARemitter and the detected object and a second signal power vs beat signalfrequency peak 850 that is indicative of the relative velocity betweenthe LIDAR emitter and the reflecting object.

FIGS. 7A and 8A depict optical frequency chirps that show linear changesin optical frequency over time, however as shown in FIG. 9 a device ofthe inventive concept can produce an optical frequency chirp with anonlinear configuration. As shown, such an optical frequency chirp canhave a first segment showing a sigmoidally trending change in opticalfrequency over time and a second segment showing a symmetric (theoppositely oriented) sigmoidally trending change in optical frequencyover time. As shown, such an optical frequency chirp 910 can also changein amplitude 920 during the duration of the chirp (for example,increasing rapidly in amplitude during the initial portion of theoptical frequency chirp and decreasing rapidly in amplitude over thefinal portion of the optical frequency chirp). Inventors have found thatthe use of such optical frequency chirps provides improved resolutionand signal to noise ratios, while reducing lobe formation.

FIG. 10 provides a schematic depiction of an FMCW LIDAR system of theinventive concept. In some embodiments of the inventive concept such asystem can be divided into two or more subsystems. In the example shown,the FMCW LIDAR 1000 is divided into four subsystems. One subsystem 1010can include a laser assembly 1015 that includes a laser source that isoptically coupled to a modulatable WGM resonator to provide a narrowlinewidth laser output, and also includes a detector assembly 1120 thatincludes at least two photocells and an amplifier that can serve tointegrate the outputs from the photocells in the form of electronicdata. An optical transfer device 1025 (for example, a waveguide)provides optical communication between the laser assembly and thedetector assembly. In some embodiments that laser assembly and thedetector assembly can be present as separate and distinct subsystems.

The laser assembly 1015 is also in optical communication 1035 with anemitter/receiver subassembly 1030 that includes an emitter thattransmits an optical chirp generated by the laser assembly into theenvironment, and a receiver that receives reflected chirps. The receiveris similarly in optical communication 1040 with the detector assembly1020. A controller subassembly 1045 can provide control functions to thelaser assembly 1015 and/or the emitter/receiver subassembly 1030. Forexample, electronic communication 1050 between the controller subsystem1045 and the laser assembly 1015 can provide modulation of the WGMoptical resonator (for example, via a resistive heater, one or morepiezoelectric actuator(s), and/or one or more electrical contact(s) togenerate an optical chirp. Such a controller subsystem can also be inelectronic communication 1055 with an emitter/receiver subsystem 1030 inorder to provide control over operations related to direction and/orscanning of the emitted chirp. Such a controller subassembly 1045 canalso control the functions of additional components, such as one or moreoptical switches that are integrated into lines of opticalcommunication. In some embodiments separate and distinct controllersubassemblies can be used to control different aspects of the FMCW LIDARsystem. For example, separate controller subassemblies can be utilizedto control the laser assembly 1015 and the emitter/receiver subassembly1030.

Electronic data provided by the detector system 1020 is also providedwith electronic communication 1060 with a data analysis subsystem 1065.Such a data analysis subsystem can include one or more processingmodules, which can incorporate one or more microprocessors. Examples ofsuitable microprocessors include members of the SnapDragon® chips fromQualComm®. For example, the data analysis subsystem 1065 can include afast Fourier transform module for initial processing of combined datafrom reflected chirps received from the environment and a reference,non-reflected chirp. The transformed data from such a fast Fouriertransform module can then be provided to a processing module forderivatization of spatial coordinates and/or velocity of a reflectivesurface that provided the reflected chirp. Such a processing module canalso derive secondary information regarding properties of the reflectivesurface (for example, color, composition, texture, etc.). The dataanalysis subsystem 1065 can store and/or transmit such data derived fromone or more reflected chirps in the form of a point cloud (i.e. acollection of data points representing spatial coordinates of reflectingsurfaces). Such a point cloud can also encode information related tovelocity and/or secondary information.

In some embodiments of the inventive concept all subassemblies depictedin FIG. 10 are provided on a single operational surface (e.g. a circuitboard, a silicon chip, etc.). In other the subassemblies can bedistributed among two or more operational surfaces. In still otherembodiments each subassembly is provided on a unique operationalsurface. In embodiments in which subassemblies are distributed amongdifferent operational surfaces, communication can be provided using aphysical medium (for example, a wire or lead) or can be provided bywireless communication (for example, WiFi, Bluetooth, IR, RF, etc.).Such wireless communications can be utilized in a distributed FMCW LIDARsystem, where subassemblies are not collocated.

In some embodiments, a LIDAR of the inventive concept is integrated intoa vehicle assistance system. In such an embodiment the LIDAR integratedinto or mounted on (or in) a mobile vehicle (for example, an automobile,an aircraft, a drone, and/or a watercraft). In such an embodiment FMCWLIDAR can provide spatial data related to position and/or velocity ofreflecting objects within the scanning range of the LIDAR system. Such ascanning range can represent a plane and/or a volume, depending upon theconfiguration of the LIDAR system. Such data can be represented as apoint cloud, wherein each point represents at least 2D or 3D spatialcoordinates related to a reflecting object. In some embodimentscharacteristics of the reflected chirp (for example, amplitude and/orintensity) can provide information related to additional characteristicsof the reflecting object (for example, composition, color, surfacetexture, etc.). Values for such additional characteristics can beencoded in the points of the point cloud.

Such point cloud data can be utilized by on-board or off-boardprocessors to provide assistance to the operation of vehicles soequipped. In some embodiments such assistance can be in the form ofwarnings and/or prompts that are provided to a vehicle operator. Such avehicle operator can be present in the vehicle, or can be piloting thevehicle remotely. In some embodiments assistance to a vehicle operatorcan be provided in the form of automated vehicle responses. Examples ofautomated vehicle responses include changes in speed (e.g. accelerating,decelerating, braking, etc.), altitude, and/or direction. Such automatedvehicle responses can be provided following prompting of the vehicleoperator or in an autonomous fashion. In some embodiments such automatedvehicle responses can override control of the vehicle provided by thevehicle operator, for example when detected conditions meet certaincriteria. Examples of such criteria include determination that adetected condition can result in injury to an operator and/or a detectedindividual, vehicle damage or loss, or require action that is more rapidthan can be provided by the operator.

In other embodiments of the inventive concept such point cloud data canbe utilized by on-board or off-board processors to provide a vehicle soequipped with the capability to operate autonomously. In someembodiments such an autonomous functionality can be at the discretion ofan onboard or remote vehicle operator. In such embodiments the vehiclecan be directed by the vehicle operator during part of its operation(for example, take off, landing, heavy pedestrian traffic, etc.) andoperate autonomously under other conditions. In other embodiments avehicle so equipped operates wholly autonomously. Such an autonomousvehicle can be configured to carry passengers (i.e. persons not involvedin operating the vehicle), or can be designed to operate without a humanpresence.

As shown in FIG. 11, a LIDAR of the inventive concept can beincorporated into an Advanced Driver Assistance System (ADAS). Suchsystems provide automated/adaptive and/or enhanced vehicle systems thatimprove safety while driving. Such systems are designed to avoidcollisions and accidents, by utilizing technologies that alert a driverto potential problems, or to avoid collisions by assuming control of thevehicle. ADAS can provide adaptive features such as automated lighting,adaptive cruise control, and automated braking, and can incorporateGPS/traffic warnings, connect with a smartphone and/or a data cloud.Such systems can alert a driver to the presence and/or proximity ofother vehicles or obstacles, keep the vehicle in a desired traffic lane,and/or provide a driver with a display of what is not visible via thevehicle's mirrors.

LIDAR devices of the inventive concept can provide an essential part ofan improved ADAS by providing a compact device that provides highlyaccurate information related to the presence, position, and/or speed ofother vehicles and of road obstacles. FIG. 11 depicts an embodiment of aLIDAR of the inventive concept that is configured for incorporation intoan ADAS. As shown, an ADAS equipped vehicle can include an FM laser thatis optically coupled to a optical resonator such that the FM laser islocked to the optical resonator by optical injection. Output of the FMlaser is modulated to provide optical frequency chirps by a chirpgenerator that is in communication with the optical resonator.Modulating the optical properties of the optical resonator provides thefrequency modulation of the optical frequency chirp via opticalinjection locking. Optical frequency chirps are provided to a beamscanner that directs the optical frequency chirp outwards and collectsthe returning echoes.

An example of an FMCW LIDAR of the inventive concept that can beincorporated into an ADAS is shown in FIG. 11. As shown in FIG. 11, anFM laser 1110 is optically coupled to an optical resonator 1120. Theoptical resonator can support one or more whispering gallery modes thatserve to entrap and/or accumulate light within the resonator. Whisperinggallery modes can correspond to one or more wavelengths of lightproduced by the FM laser. Light from the laser can be coupled into theoptical resonator by any suitable means, for example a prism or opticalfiber. Light is coupled out of the optical resonator 1120 to provideoptical injection locking of the FM laser 1110, substantially reducingits linewidth. The optical properties of the optical resonator can bechanged (for example by heat via a resistance heater, pressure via apiezoelectric device, and/or the application of a voltage potential viaan electrode), altering the wavelength associated with a whisperinggallery mode. Such an alteration is fed back to the FM laser viainjection locking to alter the output frequency of the FM laser 1110.

As shown, a chirp generator 1130 is in communication with the opticalresonator 1120. Such a chirp generator can be configured to produce oneor more chirp patterns of frequency vs time that are useful in LIDARapplications. Examples of suitable chirp patterns are described aboveand shown in FIGS. 7A, 8A, and 9. Variation of the optical properties ofthe optical resonator 1120 over time by the chirp generator 1120 resultsin the emission of optical frequency chirps from the FM laser viainjection locking of the FM laser to the optical resonator. Such opticalchirps can be transmitted to other system components, for example usingone or more optical fibers. In the example shown in FIG. 10, the opticalfrequency chirp generated by the FM laser 1110 is split into retainedand transmitted optical frequency chirps, for example using a beamsplitter. The transmitted optical frequency chirp is directed, via anoptical switch 1165 to an optical scanner 1150. Such an optical scannercan have both optical transmission and optical receiving functions, andcan utilize monostatic transmission/reception (Tx/Rx) optics.Coordination for these activities is provided, at least in part, by ascan clock 1140 that is in communication with both the optical scanner1050 and the chirp generator 1130. Such a scan clock can provide aconsistent scanning rate and or chirp generation rate, or can adjust thescanning and/or chirp generation rate depending on environmental and/ortraffic conditions. The transmitted optical frequency chirp is emittedfrom the scanner 1150 are can be returned as a reflected chirp from areflective object 1160 that lies within a scanning volume 1155 thatdefines the effective range of the LIDAR.

Reflected chirps reflected from the reflective object 1060 are directedby the scanner 1150 to a photocell/amplifier assembly 1170. A photocellof the photocell/amplifier assembly converts the reflected opticalfrequency chirp to a corresponding electrical signal that is amplifiedin the amplifier portion of the assembly. The same photovoltaiccell/amplifier assembly receives the corresponding retained chirp at adifferent photovoltaic cell, where it is converted into a correspondingelectrical signal that is similarly amplified.

Amplified electrical signals corresponding tot eh reflected chirp andthe retained chirp are processed in a fast Fourier transform engine 1175and the resulting processed data provided to a data processing engine1180 for estimation of distance between the LIDAR emitter and thereflective object, relative velocity between the LIDAR emitter and theobject, and any other relevant and derivable information. Data relatedto these parameters can be provided to an ADAS engine 1185 associatedwith vehicle and/or a point cloud 1190. Such a point cloud 1090 canserve as a repository for Cartesian coordinate and point attributesderived from the LIDAR system. Such point attributes can include scanangle, intensity of the returned signal, and other characteristics ofthe returned signal. Such data can be used to generate a model of thesurrounding environment, which can in turn be provided to the ADAS.Alternatively, data stored in the point cloud 1190 can be accessed by athird party for imaging purposes, to derive information related totraffic patterns, etc.

The ADAS engine 1185 can utilize data related to the distance andrelative speed of reflective objects outside of the vehicle to notify avehicle occupant (for example, a driver) and/or act directly on vehiclesystems. In some embodiments the ADAS engine provides a notification toa vehicle occupant. Such a notification can be an audible alarm orwarning, for example transmitted through a speaker of the vehicle'saudio system, a separate audio system, and/or an earpiece worn by thevehicle operator. In other embodiments the notification can be providedby a visual display that can be seen by a vehicle occupant. Such avisual display can include a dedicated display for this purpose, adisplay of the vehicle's navigation system, a display integrated into amirror of the vehicle, and/or a “heads up” display reflected from theinterior of a vehicle window.

In other embodiments the ADAS engine 1185 can provide instructions tosystems that influence the movement of the vehicle directly. Forexample, the ADAS engine can provide instructions that trigger anactuator that manipulates components of the vehicle's brake system,steering system, and/or engine accelerator. In such an embodiment thesystem can augment a vehicle operator's actions or, alternatively,permit the vehicle to operate in an autonomous or semi-autonomousfashion. In other embodiments the ADAS engine can provide instructionsto a vehicle system that is, at least in part, operating the vehicle.For example, such an ADAS engine can provide instructions to a cruisecontrol system, which in turn provides instructions to actuators coupledto various vehicle operating components. Alternatively, such an ADASsystem can provide instructions to an autonomous driving system thatoperates the vehicle without the benefit of a vehicle operator.

Although FIG, 11 shows an application of a LIDAR of the inventiveconcept to an ADAS, it should be appreciated that it has utility innumerous other applications. Examples include remote piloted andautonomous drones, agriculture, forestry, terrain mapping, warehousemanagement, augmented and virtual reality (VR) systems, construction,and structural sensors.

It should be apparent to those skilled in the art that many moremodifications besides those already described are possible withoutdeparting from the inventive concepts herein. The inventive subjectmatter, therefore, is not to be restricted except in the spirit of theappended claims. Moreover, in interpreting both the specification andthe claims, all terms should be interpreted in the broadest possiblemanner consistent with the context. In particular, the terms “comprises”and “comprising” should be interpreted as referring to elements,components, or steps in a non-exclusive manner, indicating that thereferenced elements, components, or steps may be present, or utilized,or combined with other elements, components, or steps that are notexpressly referenced. Where the specification claims refers to at leastone of something selected from the group consisting of A, B, C . . . andN, the text should be interpreted as requiring only one element from thegroup, not A plus N, or B plus N, etc.

What is claimed is:
 1. A system, comprising: a laser source configuredto emit light; a whispering gallery mode optical resonator that isoptically coupled to the laser source, the whispering gallery modeoptical resonator receives the light emitted by the laser source andreturns feedback light to the laser source, wherein a range offrequencies of the feedback light is based on an optical property of thewhispering gallery mode optical resonator; and a transducer coupled tothe whispering gallery mode optical resonator, the transducer isconfigured to alter the optical property of the whispering gallery modeoptical resonator; wherein the laser source is locked to the whisperinggallery mode optical resonator by optical injection utilizing thefeedback light, and wherein the laser source locked to the whisperinggallery mode optical resonator is configured to generate an opticalchirp.
 2. The system of claim 1, wherein the optical property of thewhispering gallery mode optical resonator configured to be altered bythe transducer is refractive index.
 3. The system of claim 1, whereinthe whispering gallery mode optical resonator has a spherical shape. 4.The system of claim 1, wherein the whispering gallery mode opticalresonator has a solid toroidal shape.
 5. The system of claim 1, whereinthe whispering gallery mode optical resonator has a disc shape.
 6. Thesystem of claim 1, wherein the whispering gallery mode optical resonatorhas a ring shape.
 7. The system of claim 1, further comprising: acontroller configured to apply a time-varying signal to the transducerover a period of time, the time-varying signal controls modulation ofthe optical property of the whispering gallery mode optical resonatorduring the period of time such that the range of frequencies of thefeedback light are modulated during the period of time to cause thelaser source to generate the optical chirp.
 8. The system of claim 1,wherein the laser source, the whispering gallery mode optical resonator,and the transducer are on a common substrate.
 9. The system of claim 1,further comprising: a waveguide, wherein the waveguide optically couplesthe laser source and the whispering gallery mode optical resonator. 10.The system of claim 1, further comprising: a detector assembly thatcomprise a photovoltaic cell, the photovoltaic cell is configured toconvert a reflected optical frequency chirp to a correspondingelectrical signal.
 11. The system of claim 1, further comprising: atransmitter assembly configured to transmit the optical chirp from thesystem; and a receiver assembly configured to receive a reflectedoptical chirp.
 12. The system of claim 11, further comprising: aprocessor configured to generate position data for an object external tothe system based on the reflected optical chirp.
 13. The system of claim1, wherein the range of frequencies of the feedback light is narrowerthan a range of frequencies of the light emitted by the laser source.14. The system of claim 1, wherein the system is included as part of anautonomous vehicle.
 15. An autonomous vehicle, comprising: a lidarsystem, comprising: a laser source configured to emit light; awhispering gallery mode optical resonator that is optically coupled tothe laser source, the whispering gallery mode optical resonator receivesthe light emitted by the laser source and returns feedback light to thelaser source, wherein a range of frequencies of the feedback light isbased on an optical property of the whispering gallery mode opticalresonator; a controller configured to output a time-varying signal thatcontrols modulation of the optical property of the whispering gallerymode optical resonator during a period of time such that the range offrequencies of the feedback light are modulated during the period oftime to cause the laser source to generate an optical chirp; atransmitter assembly configured to transmit the optical chirp from thelidar system; a receiver assembly configured to receive a reflectedoptical chirp at the lidar system; and a processor configured togenerate position data for an object external to the autonomous vehiclebased on the reflected optical chirp; and an engine, wherein the engineis controlled at least in part based on the position data for the objectexternal to the autonomous vehicle.
 16. The autonomous vehicle of claim15, wherein the laser source is locked to the whispering gallery modeoptical resonator by optical injection utilizing the feedback light togenerate the optical chirp.
 17. The autonomous vehicle of claim 15,wherein the whispering gallery mode optical resonator has one of aspherical shape, a solid toroidal shape, a disc shape, or a ring shape.18. The autonomous vehicle of claim 15, further comprising: a steeringsystem, wherein the steering system is controlled at least in part basedon the position data for the object external to the autonomous vehicle.19. The autonomous vehicle of claim 15, further comprising: a brakingsystem, wherein the braking system is controlled at least in part basedon the position data for the object external to the autonomous vehicle.20. A method of utilizing a lidar system, comprising: controlling alaser source of the lidar system to emit light, wherein the laser sourceis optically coupled to a whispering gallery mode optical resonator ofthe lidar system, wherein the whispering gallery mode optical resonatorreceives the light emitted by the laser source and returns feedbacklight to the laser source, and wherein a range of frequencies of thefeedback light is based on an optical property of the whispering gallerymode optical resonator; controlling modulation of the optical propertyof the whispering gallery mode optical resonator during a period of timesuch that the range of frequencies of the feedback light are modulatedduring the period of time to cause the laser source to generate anoptical chirp; transmitting the optical chirp from the lidar system;receiving a reflected optical chirp at the lidar system; and generatingposition data for an object external to the autonomous vehicle based onthe reflected optical chirp.